Protoplast fusion between incongruent Solanum bulbocastanum and S. tuberosum haploids was accomplished to produce hybrids combining elite traits from both parents. We identified 11 somatic hybrids out of 42 regenerants analyzed through ISSR markers. Some hybrids had loss or gain of fragments compared to the parents, likely due to rearrangements and deletions of chromosome segments after fusion, and/or to somaclonal variation during hybrid regeneration. Increased heterotic vigor for some traits as well as high diversity was observed as the effect of both ploidy and fusion combination. Microsporogenesis analysis indicated the occurrence of multivalent configurations and several meiotic abnormalities, such as chromosomes bridges and various spindle orientations. Since all hybrids were sterile, in vitro anther culture was employed for haploidization as a possible strategy to overcome barriers to hybridizations. Haploids were obtained from all the tetraploid S. bulbocastanum (+) S. tuberosum somatic hybrids tested, although with differences in both the number of embryos per 100 anthers cultured and the number of differentiated green plantlets. This is the first report on the successful production of haploid plants from S. bulbocastanum (+) S. tuberosum hybrids.

Brassinosteroids (BRs) have been proposed to increase the resistance of plants to drought stress. The effect of foliar application of 0.1 μM 24-epibrassinolide (EBR) on chlorophyll (Chl) content, photosystem 2 (PS 2) photochemistry, membrane permeability, lipid peroxidation, relative water content (RWC), proline content, and the antioxidant system in drought-stressed Chorispora bungeana plants was investigated. The results showed that polyethylene glycol (PEG) induced water stress decreased RWC, Chl content and variable to maximum Chl fluorescence ratio (F_v/F_m) less in plants pretreated with EBR than in non-pretreated plants. In addition, lipid peroxidation, measured in terms of malondialdehyde content, membrane permeability and proline content in drought-stressed plants were less increased in EBR pretreated plants, while antioxidative enzyme activities and reduced ascorbate and glutathione contents were more increased in EBR pretreated than in non-pretreated plants. These results suggested that EBR could improve plant growth under drought stress

Sodium/proton antiporter activity in the plasma membrane and tonoplast of cucumber seedling roots treated with 200 mM NaCl for 24 h was determined. It was observed that plasma membrane and tonoplast antiporter activity was only present in membranes from salt-treated plants. In addition, the plasma membrane antiporter protein was present in membranes after induction with NaCl, whereas tonoplast antiporter protein was observed in control and at elevated level in NaCl-treated plants. Moreover, based on the affinity of studied antiporter proteins to sodium ions, it could be assumed that excess sodium ions are firstly translocated from the cytosol to the vacuole and then excluded to the apoplast through the plasma membrane.

The influence of abscisic acid (ABA) on plastidial and cytosolic terpenoids and on two key enzymes for terpenoid biosynthesis was determined in vegetative stage of Cannabis sativa L. Low concentration of ABA (1 μM) increased 1-deoxy-D-xylulose 5-phosphate synthase (DXS) activity in treated plants in comparison to control plants. The amounts of chlorophyll a and carotenoids increased in response to ABA treatment but chlorophyll b content declined. The accumulation of α-tocopherol was stimulated only by 10 μM ABA. The ABA-treated plants showed a decline in 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) activity which was followed by a decrease in squalene and phytosterol content. ABA also decreased tetrahydrocannabinol (THC) and cannabidiol (CBD) contents. The essential oil had higher ratios of monoterpenes to sesquiterpenes as ABA-treated plants had less numbers of sesquiterpenes in comparison with control plants. Influence of ABA on the amounts of sesquiterpenes was different, some of them showed decrease of content and others increase of content.

Fluctuation in proline content is a widespread phenomenon among plants in response to heavy metal stress. To distinguish between the participation of water deficit and copper on changes in proline metabolism, potted plants and floating leaf discs of tobacco were subjected to CuSO₄ treatments. The application of copper increased the proline content in the leaves concomitantly with decreased leaf relative water content and increased abscisic acid (ABA) content in the potted plant. Excess copper increased the expression of two proline synthesis genes, pyrroline-5-carboxylate synthetase (P5CS) and ornithine aminotransferase (OAT) and suppressed proline catabolism gene, proline dehydrogenase (PDH). However, in the experiment with tobacco leaf discs floating on CuSO₄ solutions, the excess copper decreased proline content and suppressed the expression of the P5CS, OAT and PDH genes. Therefore, proline accumulation in the potted tobacco plants treated with excess Cu treatment might not be the consequence of the increased copper content in tobacco leaves but rather by the accompanied decrease in water content and/or increased ABA content.

The aim of this study was to evaluate the growth and development of Aechmea blanchetiana Baker L.B. Sm. in vitro on medium with 0.0, 0.145, 1.45 and 14.5 μM Cu and 0.0, 2.75, 27.5 and 275 μM Zn. Significant accumulation of Cu and Zn occurred at 14.5 μM Cu and 27.5 and 275 μM Zn, respectively, and there were no significant changes in contents of the other macro- and micronutrients. Superoxide dismutase (SOD) activity significantly changed in the presence of both metals. Spermine content increased as Zn concentration increased and decreased with increasing concentrations of Cu. There was an accumulation of H₂O₂ in the leaf tissue of plants grown in 1.45 and 14.5 μM Cu and 27.5 and 275 μM Zn. A. blanchetiana was found tolerant to the Cu and Zn in concentrations used in this study and displays the capacity to accumulate these metals.

The aim of this study was to test the hypothesis that salinity can affect indirectly the nitrate acquisition by a negative modulation triggered by glutamine accumulation. Cowpea plants were exposed to a mild NaCl concentration (50 mM) in order to restrict growth and N-demand. After 21 d, pretreated plants and control plants were supplied with 0, 5 and 10 mM of Ca(NO₃)₂ for 3 d in absence of NaCl. Salt pretreated plants showed a great limitation in acquisition of NO₃ ^-, indicated by decline in the nitrate uptake rate, NO₃ ^- accumulation, nitrate reductase activity and protein content. The restriction of NO₃ ^- utilization was positively associated with increased glutamine synthetase activity and glutamine accumulation, especially in roots.

An efficient in vitro regeneration protocol was developed for medicinally important aromatic plant Anethum graveolens. Nodal segments were cultured onto Murashige and Skoog (MS) basal medium supplemented with different auxins and cytokinins singly as well as in combinations. The optimum callus induction (93.33 %) was obtained on medium fortified with 2.2 μM N⁶-benzyladenine (BA) and 0.21 μM α-naphthaleneacetic acid. The best shoot regeneration (85.7 %) with 12.86 shoots per explant was achieved in two weeks when callus was subcultured on MS medium amended with 2.2 μM BA and 1.85 μM kinetin. The average length of regenerated shoots varied from 3.15 to 4.8 cm. The rooting of regenerated shoots was nearly 100 % on 1/4 MS augmented with 4.9 μM indolebutyric acid with a maximum root length of 5.1 cm. Plantlets were successfully acclimatized with 60 % survival rate. During organogenesis, catalase and ascorbate peroxidase activity increased while superoxid dismutase activity decreased. Clonal fidelity of in vitro raised plants has been checked by random amplified polymorphic DNA using 10 selected decamer primers. It has been found that regenerated plants are true to type plants.

The functions of cytosolic heat shock protein AtHsp90.3 in response to heavy metal stress were characterized by using expression of AtHsp90.3 gene in yeast and Arabidopsis thaliana. AtHsp90.3 supported the Saccharomyces cerevisiae Hsp90 knockout strain R0005 growth and maintaining cells membrane integrity under cadmium and arsenic stresses, which was compatible with the components of ScHsc82 machinery. However, constitutive overexpression of AtHsp90.3 in Arabidopsis impaired plant tolerance to Cd stress with lower germination rate and shorter root length, decreased contents of phytochelatins (PCs) and glutathione (GSH), inhibited activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD), and increased content of malondialdehyde (MDA). These results suggested that proper homeostasis of Hsp90 was critical for cellular response and/or tolerance to heavy metal stress in plants.

To investigate a possible involvement of nitric oxide in gene regulation of glutathione and flavonoid synthesis pathways, maize seedlings were treated with sodium nitroprusside (SNP), a NO donor, and apocynin (APO), an inducer of NO production. After 12-h treatment, the transcripts of γ-glutamylcysteine synthetase (γ-ecs), glutathione synthetase (gsh-s), chalcone synthase (chs), phenylalanine ammonia lyase (pal.1), myb-related protein P (P1) and actin 1 (act) genes were quantified in maize leaves by real time PCR, using α-tubulin as standard transcript. The level of γ-ecs and gsh-s transcripts in maize leaves were increased 9-fold and 12-fold, respectively, following SNP treatment, while after APO treatment, those transcripts were not significantly different from control plants. SNP-treated maize leaves did not show significant changes in pal.1 and chs expression. NO content in maize leaves was increased in SNP and APO treated plants in comparison to control plants. In conclusion, our experiments suggested that genes involved in glutathione synthesis could be modulated by SNP in maize leaves. On the other hand, APO had no effect on γ-ecs and gshs gene expression.

Cucumber seedlings were pretreated with 3 μM 5-aminolevulinic acid (ALA) followed by cultivation at normal (25/18 °C) or high (42/38 °C) day/night temperature to investigate the protective effects of ALA on heat stress in plants. Heat elevated the contents of malondiadehyde (MDA), superoxide radical (O₂ ^.-) and hydrogen peroxide (H₂O₂) in leaves of all plants but less in ALA-pretreated plants. Heat treatment resulted in higher antioxidant enzyme activities and proline and soluble sugar contents and weaker growth inhibition in ALA-pretreated plants than in those treated with heat alone. These results indicate that ALA pretreatment increased the tolerance of seedlings to heat stress.

The accumulation of cold-induced dehydrin and proline was related to the frost tolerance (FT) in several Brassica species or cultivars. A dehydrin of molecular mass 47 kDa was detected in the leaves of an Ethiopian mustard (B. carinata) and a pair of dehydrins of similar molecular mass in the three (two winter, one spring) oilseed rape (B. napus) cultivars, when plants were maintained at 4 °C for one-month under two different irradiances. More dehydrin was accumulated in oilseed rape than in Ethiopian mustard under the high irradiance. A significant correlation was observed between leaf dehydrin content and FT, and no relationship between proline content and FT or between the proline and dehydrin contents. Protoplast-derived callus cells behaved differently from leaves sampled from intact plants, as they did not accumulate dehydrin and proline in response to cold stress.

Short-term responses of Sedum alfredii roots to Cd exposure was compared in Cd hyperaccumulator (HE) and nonhyperaccumulating ecotype (NHE). Cadmium exposure significantly inhibited root elongation and induced loss of plasma membrane integrity and lipid peroxidation of roots tips in the NHE, whereas these effects were much less pronounced in the HE plants. A strong accumulation of reactive oxygen species with increasing Cd concentration was noted in the NHE root tips, but not in HE. After Cd exposure, a dose-dependent decrease in oxidized glutathione and marked increase in reduced glutathione and non-protein thiols were observed in root tips of HE, but were not seen in the NHE plants. These results suggest that the HE tolerates high Cd in the environment through the differential adaptations against Cd-induced oxidative stress.

The Potato virus X (PVX)-based vector was used for the construction of N- and C-terminally modified PVX coat protein (XCP) chimeras. N-terminal XCP modifications do not influence the viral life cycle, whereas the simple XCP C-terminal fusion impedes the viral replication. We designed several C-terminally modified XCP chimeras and tested their viabilities in various Nicotiana benthamiana genotypes. Our results showed the negative impact of 3'-terminal modification of XCP on the chimera's life cycle. To ensure chimeric constructs stability, the second copy of the last 60 nucleotides of XCP followed by the 3'-untranslated region (UTR) was added downstream of the recombinant sequence. Simultaneously, the first copy of the last 60 nucleotides of XCP was mutated in order to prevent recombination between the two identical sequences. The movement protein of Tobacco mosaic virus expressed in transgenic N. benthamiana plants positively affected the cell-to-cell spread of C-terminally modified XCP chimeras.

To uncover the potential antioxidative role of anthocyanins in vivo in protecting photosynthetic tissues from photoinhibition, the effects of high irradiance [HI, 1300 μmol(photon) m^-2 s^-1] were studied using detached leaves derived from Arabidopsis wild-type (WT) and the mutant deficient in anthocyanin biosynthesis (tt3tt4). HI stress caused decreased chlorophyll content and photochemical efficiency, but increased cell-membrane leakage and contents of hydrogen peroxide and superoxide radical in the leaves of both Arabidopsis phenotypes, but the WT plants showed better HI tolerance than tt3tt4 mutant. HI caused a significant increase in the 1,1-diphenyl-2-picrylhydrazyl scavenging capacity in WT but not in the tt3tt4 mutant. The anthocyanins could not contribute substantially to light-shielding during the periods of HI stress, because the anthocyanin content in WT was very low and the colour of leaves was the same as in the tt3tt4 mutant. Thus, it was assumed that the better HI tolerance in WT was mostly related to the potential antioxidative role of anthocyanins.

The potential of 5-aminolevulenic acid (ALA) to enhance the salt tolerance of cucumber (Cucumis sativus L.) seedlings was investigated. ALA was applied at various concentrations (0, 1, 10, 25, 50, and 100 mg dm^-3) as foliar spray or root watering. Then the seedlings were exposed to 0 or 75 mM NaCl for 5 d. NaCl stress reduced the root and leaf dry masses, leaf area, and the leaf net CO₂ assimilation rate. These reductions were counteracted by exogenous ALA, and the most efficient was 50 mg dm^-3 concentration via foliar spray. ALA decreased the H₂O₂ contents and increased the activities of ascorbate peroxidase (APX) and glutathione reductase (GR) in NaCl-treated cucumber roots and leaves and the activity of catalase (CAT) in leaves. The ALA application also up-regulated the expressions of CAT and cAPX genes in roots and leaves and the expression of GR gene in roots of the NaCl treated cucumber plants.

A new plant expression vector (pBSbtCry1Ac-GNA) containing two insect resistant genes, a synthetic chimeric gene SbtCry1Ac encoding the insecticidal protein CrylAc and a gene GNA encoding snowdrop lectin (Galanthus nivalis agglutinin) was constructed. Transgenic tobacco plants containing these two genes were obtained through Agrobacterium-mediated transformation of tobacco leaf discs. Results from PCR detection and genomic DNA Southern blot analysis indicated that both SbtCrylAc gene and GNA gene were integrated into the genome of these plants. Results of Western blot analysis indicated that these two proteins were expressed in the analyzed plants. Bioassays of Myzus persicae and Helicoverpa assulta on detached leaves of transformed tobacco plants were carried out. The average aphid inhibition rate of these plants tested at 12 d post-infestation was 71.9 %. The average H. assulta mortality of these plants tested at 6 d post-infestation was up to 89.8 %. The kanamycin resistance of the T₁ progeny of these transgenic plants was analyzed and a typical 3:1 segregation was observed.

DNA cassette consisting of an Arabidopsis dehydration-responsive element binding factor 1 (DREB1B) cDNA, driven by a cauliflower mosaic virus 35S promoter, was introduced into potato plants (Solanum tuberosum L.) through Agrobacterium tumefaciens-mediated gene transfer. The presence and expression of the gene in transgenic plants were confirmed by the PCR and RT-PCR techniques, respectively. Northern hybridization using a DREB1B cDNA probe revealed high levels of DREB1B expression among the most transgenic lines. Overexpression of DREB1B imparted a significant freezing and drought tolerance gain in the transgenic potato lines. In comparison with the wild-type plants, the transgenic potatoes contained higher proline content under drought and freezing conditions, and maintained their relative water content higher under water stress. The enhancement of tolerance in transgenic potato highlights the presence of genes responding to the transcription factor DREB1B in this plant.

We investigated the drought resistance of a wheat (Triticum aestivum L.) stay-green mutant tasg1 and its wild-type (WT) in field experiments conducted for two years. Drought stress was imposed by controlling irrigation and sheltering the plants from rain. Compared with the WT, tasg1 exhibited a distinct delayed senescence under both normal and drought stress conditions, as indicated by slower degradation of chlorophyll and decrease in net photosynthetic rate than in WT. At the same time, tasg1 mutants maintained more integrated chloroplasts and thylakoid ultrastructure than did WT plants under drought stress. Lower malondialdehyde content and higher antioxidative enzyme activities in tasg1, compared to WT, may be involved in the stay-green phenotype and drought resistance of tasg1.

The effects of exogenous 24-epibrassinolide (EBR) on the growth, oxidative damage, antioxidant system and ion contents in eggplant (Solanum melongena L.) seedlings under salt stress were investigated. Eggplant seedlings were exposed to 90 mM NaCl with 0, 0.025, 0.05, 0.10 and 0.20 mg dm^-3 EBR for 10 d. EBR, especially at concentration 0.05 mg dm^-3, alleviated growth suppression caused by NaCl stress, decreased electrolyte leakage, superoxide production and content of malondialdehyde and H₂O₂ in NaCl-treated plants. EBR also increased activities of superoxide dismutase, guaiacol peroxidase, catalase and ascorbate peroxidase and the contents of ascorbic acid and reduced glutathione. Furthermore, we also found that Na⁺, Cl^- contents were decreased, K⁺, Ca²⁺ contents and K⁺/Na⁺, Ca²⁺/Na⁺ ratios were increased in the presence of EBR under salt stress.

Transgenic Citrus sinensis (L.) Osb. plants, cvs. Valencia and Hamlin, expressing Citrus tristeza virus (CTV) derived sequences were obtained by genetic transformation. The gene constructs were pCTV-CP containing the 25 kDa major capsid protein gene (CTV-CP), pCTV-dsCP containing the same CTV-CP gene in an intron-spliced hairpin construct, and pCTV-CS containing a 559 nt conserved region of the CTV genome. The transgenic lines were identified by PCR and the transgene integration was confirmed by Southern blot. Transgene mRNA could be detected in most transgenic lines containing pCTV-CP or pCTV-CS transgene. The mRNA of pCTV-dsCP transgene was almost undetectable, with very light bands in most analyzed plants. The transgene transcription appears to be closely linked to the type of gene construct. The virus challenge assays reveals that all transgenic lines were infected. However, it was possible to identify propagated clones of transgenic plants of both cultivars studied with a low virus titer, with values similar to the noninoculated plants (negative control). These results suggested that the transgenic plants present some level of resistance to virus replication. The higher number of clones with low virus titer and where mRNA could not be detected or was presented in a very light band was found for pCTV-dsCP-derived transgenic lines.

Ferns present two alternant generations: sporophyte and gametophyte. In the present work we address the question of whether fern gametophytes have the potential to acclimate to different irradiances as vascular plants do. We studied the gametophytes of three different fern species belonging to the Aspleniaceae family with different ecological requirements (Asplenium trichomanes, Asplenium scoloprendrium and Ceterach officinarum). Fern spores were germinated and the gametophytes cultivated under photon flux density (PFD) of 10, 50 or 100 μmol m^-2 s^-1. From the early stages of spore germination (the formation of the 5-celled germinal filament), photosynthetic apparatus acclimates showing the typical patterns of photochemical responses to high or low PFD. In agreement with the photochemical pattern of acclimation, higher contents of xanthophyll cycle pigments and α-tocopherol was observed in plants grown under high PFD. The α/β-carotene ratio, used as indicator of the acclimation of the photosynthetic apparatus, also sustained the initial hypothesis except for A. trichomanes. We conclude that fern gametophytes display a complete array of photosynthetic and photoprotective traits that allow an effective acclimation to PFD.

Zinc finger proteins are encoded by the genes chiefly involved in stress resistance hormone signal transduction of plants. In this study, a cDNA encoding a zinc finger transcription factor was isolated by the yeast one-hybrid system from Gossypium arboreum using the MYB-box element of the universal stress gene (GUSP1) promoter as bait. The corresponding protein (named GaZnF) can bind specifically to a 13 bp MYB-box region. The GaZnF cDNA is 1093 bp in length, including a 510 bp open reading frame. The predicted GaZnF protein contains ANI-A20 motifs and shares a high sequence similarity with zinc finger proteins from other plants. Spatial expression pattern of GaZnF was studied under drought, heavy metals and salt stresses through real-time PCR. The gene showed enhanced expression under each stress treatment with maximum transcript abundance in root tissues. The results support the hypothesis that G. arboreum zinc finger proteins are involved in plant response to drought, salt and heavy metal stresses.

Ultraviolet-B radiation (biologically effective dose 2.6 kJ m^-2 d^-1) had negative influence on morphology and physiology of the young triticale plants. Plants exposed to UV-B were of lower height than control plants, their leaves were narrow, and the rate of net photosynthesis was decreased. The line RAH 336, which wax cover is lesser than that of traditional cultivar Magnat, was more susceptible to UV-B radiation, considering primary photosynthesis reactions, recorded by chlorophyll a fluorescence. An activation of protective mechanisms was observed: plants responded to UV-B by an increase of the content of UV-B absorbing compounds, and changes of antioxidant enzyme activities.

As an initial step towards understanding the molecular mechanisms by which plants become invasive, we present here the first transcriptome analysis for an invasive weed Mikania micrantha. The analysis was based on the 75-nucleotide short reads data generated by the Illumina Genome Analyzer II system. A total of 31 131 unique sequences were assembled de novo based on 8.7 million filtered paired-end sequence reads for the transcriptome of an individual M. micrantha growing in the field. 73 % of the unique sequences showed significant similarity to existing proteins in the NCBI database, and 21 448 could be grouped based on gene ontology assignments. Of particular interest are the sequences that share homology with genes involved in genome evolution, plasticity, secondary metabolism and defense responses.

Glucose-6-phosphate dehydrogenase (G6PDH) has been implicated in supplying reduced nicotine amide cofactors for biochemical reactions and in modulating the redox state of cells. In this study, the role of G6PDH in thermotolerance of the calli from Przewalskia tangutica and tobacco (Nicotiana tabacum L.) was investigated. Results showed that Przewalskia tangutica callus was more sensitive to heat stress than tobacco callus. The activity of G6PDH and antioxidant enzymes (ascorbate peroxidase, catalase, peroxidase and superoxide dismutase) in calli from Przewalskia tangutica and tobacco increased after 40 °C treatment, although two calli exhibited a difference in the degree and timing of response to heat stress. When G6PDH was partially inhibited by glucosamine pretreatment, the antioxidant enzyme activities and thermotolerance in both calli significantly decreased. Simultaneously, the heat-induced H₂O₂ content and the plasma membrane NADPH oxidase activity were also reduced. Application of H₂O₂ increased the activity of G6PDH and antioxidant enzymes in both calli. Diphenylene iodonium, a NADPH oxidase inhibitor, counteracted heatinduced H₂O₂ accumulation and reduced the heat-induced activity of G6PDH and antioxidant enzymes. Moreover, exogenous H₂O₂ was effective in restoring the activity of G6PDH and antioxidant enzymes after glucosamine pretreatment. Western blot analysis showed that G6PDH gene expression in both calli was also stimulated by heat and H₂O₂, and blocked by DPI and glucosamine under heat stress. Taken together, under heat stress G6PDH promoted H₂O₂ accumulation via NADPH oxidase and the elevated H₂O₂ was involved in regulating the activity of antioxidant enzymes, which in turn facilitate to maintain the steady-state H₂O₂ level and protect plants from the oxidative damage.

Xylem sap outflow from fine lateral roots (FLRs) isolated from hydroponically grown young maize (Zea mays L.) plants was visualized by local brightening of test solutions contrasted with purified Indian ink particles. Flow into the vessels was indicated by the adsorption of Evans Blue in their walls. The fraction of the FLRs able to exude xylem sap in a mineral medium with 30 mM mannitol decreased with increasing incubation time. This change was strongly retarded, when the FLRs were incubated in a medium containing glucose instead of mannitol. There was a broad range of variation of the osmotic potential of the test solutions (Ψ_so), wherein the fraction of the FLRs showing an initially reversed flow of the xylem sap varied between zero and unity. A median (M) of the osmotic potential of the xylem sap in FLRs (Ψ_sx) was estimated. It represents the value of Ψ_so that was lower than Ψ_sx in half of the roots of a sample before their transfer to the test solutions (Ψ_sxo). M was dependent on the osmotic potential of the medium used for growth or pre-incubation of the FLRs. Its value was not dependent on the molecular size of the osmolytes used to adjust Ψ_so, including dextran 8, which is excluded from cell walls. In all of the studied plants, M was lower than the osmotic potential of the xylem sap collected from the root before isolation of the FLRs. To explain this finding it is assumed that FLRs with Ψ_sxo > M had a higher hydraulic conductivity and a larger volume contributed to the exuded sap than those with Ψ_sx < M.

The effects of lead toxicity on leaf gas exchange, chlorophyll content, chlorophyll fluorescence, chloroplast ultrastructure, and opening of stomata were examined in tobacco (Nicotiana tabacum L.) plants. Plants were grown in a growth chamber for 7 d in Hoagland nutrient solution supplemented with 0.0 (control), 5, 10, 25, 50, 100, 300 and 500 μM Pb(NO₃)₂. Plants treated with 5, 10, and 25 μM Pb(NO₃)₂ exhibited no abnormalities. Root and shoot growth, net photosynthetic rate and stomatal conductance were significantly reduced in plants treated with 100, 300 and 500 μM Pb(NO₃)₂. In plants treated with 500 μM Pb(NO₃)₂, the majority of stomata were closed. The effect of Pb(NO₃)₂ on chlorophyll content and chlorophyll fluorescence parameters was negligible. However, in plants exposed to 100, 300, and 500 μM Pb(NO₃)₂, the mesophyll cells showed altered chloroplasts with disrupted thylakoid membranes.

Exogenous salicylic acid has been shown to confer tolerance against biotic and abiotic stresses. In the present work the ability of its analogue, 4-hydroxybenzoic acid to increase abiotic stress tolerance was demonstrated: it improved the drought tolerance of the winter wheat (Triticum aestivum L.) cv. Cheyenne and the freezing tolerance of the spring wheat cv. Chinese Spring. Salicylic acid, however, reduced the freezing tolerance of Cheyenne and the drought tolerance of Chinese Spring, in spite of an increase in the guaiacol peroxidase and ascorbate peroxidase activity. The induction of cross tolerance between drought and freezing stress was observed: drought acclimation increased the freezing tolerance of Cheyenne plants and cold acclimation enhanced the drought tolerance. The induction of drought tolerance in Cheyenne was correlated with an increase in catalase activity.

Iron is one of the essential micronutrients required by all living organisms. In this study, we isolated a gene encoding putative citrate synthase (CS) from Malus xiaojinensis, designated as MxCS1. The MxCS1 gene encodes a protein of 473 amino acid residues with a predicted molecular mass of 52.5 kDa and a theoretical isoelectric point of 8.67. The expression of MxCS1 was enriched in the leaf rather than in phloem and root, however, its expression was hardly detected in the xylem. The gene expression was strongly induced by Fe stress treatment in the M. xiaojinensis seedlings. Over-expression of MxCS1 improved Fe deficiency tolerance in transgenic Arabidopsis. We argued that MxCS1 is a new member of the CS genes, and it may function as a regulator in response to iron stress in plants.